Effect of Sequential Burr Passes on Minimally Invasive Akin and First Metatarsal Dorsiflexion Osteotomies

Introduction/Purpose: Minimally invasive surgical (MIS) techniques for are exponentially increasing as a surgical option for treating midfoot and forefoot conditions. However, performing percutaneous osteotomies using the burr prevents direct visualization to estimate the correct measurements for the resection. This study aimed to evaluate the impact of each burr pass on the degree of correction, gap size, and alignment in MIS Akin and first metatarsal dorsiflexion osteotomies (DFO). It is hoped that this will improve the surgeon's ability to correct the desired amount of deformity and assist in surgical planning. Methods: Minimally invasive Akin and first metatarsal DFO were performed on ten cadaveric specimens using a 2 mm Shannon burr. The lateral (for Akin) and plantar (for 1st DFO) cortices were left intact. A total of 5 passes with the Shannon burr were performed during each osteotomy. The osteotomy gap was manually closed after each pass and held closed while completing the subsequent passes. Fluoroscopy images were obtained before and after each of the five passes, on which two independent reviewers performed measurements and inter-observer reliability was evaluated with ICC analysis. Measurements included the metatarsal dorsiflexion angle (MDA) and dorsal cortical length (MDCL). Likewise, the phalangeal measurements included the first phalangeal medial cortical length (PCML) and proximal to distal phalangeal articular angle (PDPAA) (Figure 1). Results: The average decrease in PCML with each burr pass was as follows: 1.53 mm at the 1st pass, 1.33 mm at the 2nd pass, 1.27 mm at the 3rd pass, 1.23 mm at the 4th pass, and 1.13 mm at the 5th pass. The MDCL sequentially decreased by 1.80 mm, 1.59 mm, 1.35 mm, 0.75 mm, and 0.60 mm. The MDA consistently decreased, and the PDPAA incrementally became more valgus oriented following each consecutive burr pass. Interobserver reliability analysis demonstrated good agreement for all parameters. Conclusion: The results revealed the length and alignment changes trends in the forefoot and midfoot osteotomies with each burr pass. On average, a first metatarsal dorsal wedge resection of 4.7 mm and first phalangeal medial wedge resection of 2.9 mm was achieved after 3 and 2 burr passes, respectively. The first burr pass provided a correction of 76% of the burr diameter, while it decreased to 66%, 63%, 61%, and 56% of the burr diameter with each subsequent pass. This data may aid surgeons determine the optimal number of burr passes required for the amount of resection needed. Overview of the radiographic measurements. A) first metatarsal dorsiflexion angle (MDA), B) first metatarsal dorsal cortical length (MDCL), C) first phalangeal medial cortical length (PCML) and D) proximal to distal phalangeal articular angle (PDPAA). The diameter of the sphere © The Author(s) 2024(Dsphere) was calculated automatically by the MATLAB script for calibration purposes.